An image sensor converts an optical image into an electric signal. Image sensor may be classified as complementary metal oxide silicon (CMOS) image sensors or charge coupled device (CCD) image sensors. The CCD image sensor has relatively higher photosensitivity and lower noise than CMOS image sensors. However, CCD image sensors are more difficult to miniaturize, and integrate with other devices. Power consumption of the CCD image sensor is also higher. On the other hand, CMOS image sensors are prepared using a more simplified process than CCD image sensors. CMOS image sensors are easier to miniaturize, and integrate with other devices. Power consumption of the CCD image sensor is also higher.
With advances in technologies for preparing semiconductor devices, technology for preparing the CMOS image sensors, and consequently the characteristics of the CMOS image sensors, have been greatly improved. Accordingly, much research has been recently carried out on the CMOS image sensor.
A pixel of the CMOS image sensor includes photodiodes for receiving light and CMOS devices for controlling image signals from the photodiodes. The photodiodes generate electron-hole pairs, depending on the wavelength and intensity of red light, green light, and blue light incident through color filters. The photodiodes change an output signal, based on the amount of electrons generated. The aggregate of output signals from the photodiodes makes possible the detection of an image.
FIG. 1 is a sectional view illustrating a related CMOS image sensor. A method of fabricating the related CMOS image sensor will be described with reference to FIG. 1.
As shown in FIG. 1, an epitaxial layer 1 is formed over a semiconductor substrate by an epitaxial process. The epitaxial layer 1 includes a plurality of photodiodes. Subsequently, a plurality of devices (not shown) for signal processing are formed, and a plurality of metal wire layers (not shown) for interconnecting the respective signal processing devices are formed. Oxide film is applied to form a device passivation layer 2 for protecting the devices from moisture or external physical impact.
A dark matrix for intercepting unnecessary light is formed over the entire surface. At present, however, color filters 3, made of positive photoresist, are used as the dark matrix to only pass light having a green wavelength. A planarization layer 4 having a plane surface is formed to support micro lenses 5, which are formed in a subsequent process.
In the method of fabricating the related CMOS image sensor as described above, the green light color filters, used as the dark matrix, intercept red light and blue light but allow green light to pass. As a result, undesired signals are generated in the CMOS image sensor.
When red light color filters, blue light color filters, and green light color filters are successively arranged to intercept all the color components of light, the color filters must have a thickness of 3 μm or more to substantially completely intercept light. In addition, a hot pixel phenomenon, in which unnecessary signals are generated due to ambient temperature, occurs in the CMOS image sensor.